It is well known that after semiconductor dies are fabricated on a semiconductor wafer, such as but not limited to, silicon or gallium arsenide, the wafer is sawn (also referred to as “diced”) to separate the individual semiconductor die (also known as “dice” or “chips” or “device”) on the wafer. These separated die are then each packaged to facilitate safe die handling, and attachment to circuit boards, heat sinks, and the like. During this process, the die is attached or mounted to a packaging substrate (also known as a “flange”). In the case of some devices, such as power amplifiers, where heat generation is expected during operation of the device, the die with packaging substrate backing is then mounted or attached to a heat sink that acts to remove generated heat by conduction away from the device in use.
In a typical packaging process, the die is attached to the flange by any suitable method, for example by soldering or using an adhesive. This process is carried out at elevated temperature, and the die-flange combination is subsequently cooled to room temperature.
For conventional materials used in packaging, such as those described in U.S. patent publication 20050016750 A1, there is a tendency for the flange to deform from planarity or “warp,” upon cooling after the die attachment process. The deformation leads to further manufacturing problems in subsequent processes when the window frame, leads and lid are attached. It also to leads to inefficient transfer of heat generated by the die, while it is in use, to the flange and heat sink. Consequently, the warpage prevents the maximum potential heat transfer from die to flange and from flange to heat sink. This leads to temperature increase at the die, with undesirable consequences.
In another configuration, U.S. patent publication 20050012118 describes a package that can withstand high die-attach temperatures and that can provide a hermetically sealed air cavity for a die, without the use of adhesives. It discusses a circuit package for housing semiconductor that has a metallic flange, one or more high-copper leads and a liquid crystal polymer frame molded to the flange and the leads. The flange includes a dovetail-shaped groove that mechanically interlocks with the molded frame. During molding, a portion of the frame forms a key that freezes in or around the frame retention feature. There is no discussion of heat-induced flange deformation.
The art recognizes that heat transfer from die to flange poses a challenge in operations where the die is attached at high temperature, and the combination is subsequently cooled to room temperature and thermal-mechanical deformation is induced.
Accordingly, it is desirable to minimize the warpage of the flange in the die attachment process. In addition, it is desirable to develop a solution that retains the highest possible heat transfer from die to flange, and from flange to heat sink. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.